The HER family receptor tyrosine kinases are important mediators of cell growth, differentiation and survival. The receptor family includes four distinct members including epidermal growth factor receptor (EGFR, ErbB1, or HER1) HER2 (ErbB2), HER3 (ErbB3) and HER4 (ErbB4). Upon ligand binding the receptors form homo and heterodimers and subsequent activation of the intrinsic tyrosine kinase activity leads to receptor auto-phosphorylation and the activation of downstream signaling molecules (Yarden and Sliwkowski). De-regulation of EGFR by overexpression or mutation has been implicated in many types of human cancer including colorectal, pancreatic, gliomas, head and neck and lung cancer and several EGFR targeting agents have been developed over the years (Ciardiello, Hynes). Erlotinib (Tarceva®), a reversible inhibitor of the EGFR tyrosine kinase was approved by the United States Food and Drug Administration (FDA) for the treatment of recurrent NSCLC and pancreatic cancer. Other reversible EGFR tyrosine kinase inhibitors (“TKI”) include gefitinib and lapatinib.
The most impressive single agent activity of EGFR tyrosine kinase inhibitors is observed in a subset of non-small cell lung cancer (NSCLC) patients whose tumors harbor somatic kinase domain mutations, whereas clinical benefit in wild-type EGFR patients is greatly diminished (Lynch 2004, Paez 2004). The most common somatic mutations of EGFR are exon 19 deletions with delta 746-750 the most prevalent mutation and the exon 21 amino acid substitutions with L858R the most frequent mutation (Sharma). Intriguingly, this is a subset of patients characterized by high prevalence of adenocarcinomas, females, never-smokers and Asians (Miller, Pao 2004).
Patients with EGFR-mutant lung cancer eventually develop disease progression after 10-14 months on EGFR tyrosine kinase inhibitors (Pao 2010). Over 50% of patients that progress on tyrosine kinase inhibitors acquire a secondary mutation in the kinase domain at position 790 that is known as the gatekeeper residue. Replacement of threonine by the bulkier residue methionine (T790M mutation) leads to an increase in the affinity for ATP relative to mutant forms of EGFR associated with clinical benefits from EGFR TKI treatment and to a reduced affinity for TKIs which taken together confers drug resistance (Yun). Similar gatekeeper mutations in the kinase domain that cause drug resistance are seen in Abl and Kit (Tamborini, Gone). The present invention demonstrates the generation of selective molecules that specifically inhibit T790M containing EGFR mutants.